1. Field of the Invention
The present invention relates to a physiological signals processing system for compressing and reproducing physiological signals such as electrocardiogram signals and electroencephalogram signals.
2. Description of the Prior Art
When diagnostication is carried out by using an electrocardiographic waveform during a clinical examination, the pattern of the waveform is conventionally often recognized by a computer. This system is roughly divided into an on-line system and an off-line system according to the process by which electrocardiographic waveform is input to the computer. According to the on-line system, the waveform derived from the human body is directly input to the electronic computer. On the other hand, according to the off-line system, the waveform data is once stored in a memory medium and is then processed collectively.
In the electrocardiographic waveform, it sometimes happens that an abnormal wave of several heartbeats (cardiac arrhythmias) temporarily appears among the continuous normal waves. In order to detect such an abnormal wave, it is necessary to always monitor a patient. Most of the patients wherein abnormal waves temporarily appear are usually normal and live in the same manner as ordinary healthy people. The off-line system such as arrhythimia detection system for an ambulatory ECG monitor or Holter-type ECG is suitable for the examination of these patients. Namely, the electrocardiographic waveform is stored in a small device that can be attached to the human body and analysis is carried out afterward.
A large memory capacity is necessary for storing an electrocardiographic waveform recorded for a long time. Therefore, it is necessary to compress the waveform data. When the waveform data is compressed, it is indispensable that any error in the waveform reproduced from the original waveform should be small and, at least, the information necessary for correct diagnosis should be stored. Furthermore, according to the off-line system, it is necessary to process the waveform in real time by a processor having a small processing capacity, and hence, the algorithm should be simple and performed at a high speed.
The AZTEC (Amplitude-Time-Zone-Epoch-Coding) system is the most widely used data-reduction technique. However, it introduces significant discontinuities and distortion of the reconstructed signals.